Light emitting diode and fabrication method thereof

ABSTRACT

A light emitting diode (LED) and a method for fabricating the same, capable of improving brightness by forming a InGaN layer having a low concentration of indium, and whose lattice constant is similar to that of an active layer of the LED, is provided. The LED includes: a buffer layer disposed on a sapphire substrate; a GaN layer disposed on the buffer layer; a doped GaN layer disposed on the GaN layer; a GaN layer having indium disposed on the GaN layer; an active layer disposed on the GaN layer having indium; and a P-type GaN disposed on the active layer. Here, an empirical formula of the GaN layer having indium is given by In(x)Ga(1-x)N and a range of x is given by 0&lt;x&lt;2, and a thickness of the GaN layer having indium is 50-200 Å.

This application is a Continuation of co-pending application No.11/889,549 filed on Aug. 14, 2007, which is a Divisional of co-pendingapplication No. 11/333,247 (now U.S. Pat. No. 7,531,827) filed on Jan.18, 2006, and for which priority is claimed under 35 U.S.C. §120; andthis application claims priority of Application No. 2003/48993 filed inKorea on Jul. 18, 2003 under 35 U.S.C. §119; the entire contents of allare hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a light emitting diode, and moreparticularly, to a light emitting diode and a fabrication method thereofin which a light efficiency can be improved by forming a layercontaining indium (In), whose lattice constant is similar to that of anactive layer formed in the LED.

BACKGROUND ART

Generally, a light emitting diode (LED) is a kind of semiconductordevice, and it converts an electrical signal into infrared ray or lightby using a characteristic of a compound semiconductor, to send orreceive a signal. The LED is used for home appliances, a remotecontroller, an electronic display board, a display device, a variety ofautomation apparatuses and the like.

An operation principle of the LED will be briefly described in thefollowing.

When a forward voltage is applied to a semiconductor of a specificchemical element, electrons and holes are recombined with each otherwhile moving through a positive-negative junction. The recombination ofthe electrons and the holes causes an energy level to fall down, so thatlight is emitted.

The LED is generally manufactured to have a very small size of 0.25 mm²and is mounted on a printed circuit board (PCB) or a lead frame using anepoxy mold.

Representative of the LEDs is a plastic package of 5 mm (T 1¾) or a newpackage being developed in a specific application field.

A color of light emitted from the LED is determined by a wavelengthobtained depending on a combination of elements constituting asemiconductor chip.

Particularly, as an information communication apparatus is in a trend ofa small-size and slimness, the communication apparatus has moreminiaturized parts such as a resistance, a condenser, and a noisefilter. The LED is manufactured in a form of a surface mounted device(hereinafter, referred to as “SMD”) so as to be directly mounted on aprinted circuit board (hereinafter, referred to as “PCB”).

Accordingly, an LED lamp for a display device is being developed in theform of the SMD. Such an SMD can substitute a related-art simple lamp.The SMD is used for a lamp display, a character display, an imagedisplay and the like that express various colors.

Further, as a high-density integration technology for a semiconductordevice is developed and a consumer prefers a more compact electronicproduct, Semiconductor Mounting Technology (SMT) is widely used, and apackaging technology of the semiconductor device employs a technologyfor minimizing an installation space such as a Ball Grid Array (BGA), awire bonding, and a flip chip bonding.

FIG. 1 is a view illustrating a process for fabricating a light emittingdiode according to the related art.

As shown in FIG. 1, a gallium nitride (GaN) buffer layer 101 is formedon a sapphire substrate 100 formed of Al₂O₃. After that, a GaN layer103, which is not doped with dopants (Hereinafter, referred to as“undoped”), is formed on the GaN buffer layer 101.

In order to form a Group 3-based element in a form of a thin film on thesapphire substrate 100 as described above, a metal organic chemicalvapor deposition (MOCVD) is generally used. At this time, the thin filmlayer is formed under a constant growth pressure.

An N-type GaN layer 105 is formed on the undoped GaN layer 103, andsilicon using silane (SiH₄ or disilane (Si₂H₆) gases is used to form theN-type GaN layer 105.

After the N-type GaN layer 105 is formed, an active layer 109 is formedon the N-type GaN layer 105. The active layer 109 functioning as a lightemission region is a semiconductor layer having an illuminant formed ofa indium gallium nitride (InGaN).

After the active layer 109 is formed, a P-type GaN layer 110 issubsequently formed.

The P-type GaN layer 110 is in a contrast to the N-type GaN layer 105.Namely, electrons are drifted by an external voltage in the N-type GaNlayer 105, while holes are drifted by the external voltage in the P-typeGaN layer 110. Therefore, the holes and the electrons are mutuallyrecombined in the active layer 109, thereby emitting light.

A transparent metal (TM) layer using a transparent Indium-Tin-Oxide(ITO) metal is formed on the P-type GaN layer 110 so that lightgenerated at the active layer 109 is transmitted and emitted to theexternal.

After the TM layer is formed, a P-type electrode is formed to completethe LED.

However, the LED constructed as above has a drawback in that a strain isincreased due to an inconsistency of the lattice constants between theInGaN layer of the active layer and the GaN layer, thereby reducing anamount of light generated in the active layer.

Further, the inconsistency of the lattice constant deteriorates aproduct reliability of the LED.

Also, there is a drawback in that the active layer, which is formed onthe N-type GaN layer adjacent to the active layer in a form of atwo-dimensional plane, has a lower luminous intensity than athree-dimensional formation.

DISCLOSURE OF THE INVENTION

Accordingly, the present invention is directed to an LED and afabrication method thereof that substantially obviate one or moreproblems due to limitations and disadvantages of the related art.

An object of the present invention is to provide an LED and afabrication method thereof in which a GaN layer having a lowconcentration of indium (In) is formed between the active layer and anN-type GaN layer to reduce an inconsistency of lattice constants betweenan active layer and a GaN layer, thereby increasing a light efficiencyand improving a product reliability.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a lightemitting diode includes: a buffer layer disposed on a sapphiresubstrate; a GaN layer disposed on the buffer layer; an N-type GaN layerdisposed on the GaN layer; a GaN layer having indium disposed on theN-type GaN layer; an active layer disposed on the GaN layer havingindium; and a P-type GaN layer disposed on the active layer.

Here, an empirical formula of the GaN layer having indium is given byIn(x)Ga(1-x)N and a range of x is given by 0<x<2, and a thickness of theGaN layer having indium is 50-200 Å.

Also, a GaN layer whose thickness is 10-30 Å is formed on the GaN layerhaving indium, and the active layer is of a multi-quantum well structurehaving a InGaN/GaN structure.

Also, a method for fabricating a LED according to the present invention,includes the steps of: forming a buffer layer on a sapphire substrate;forming a GaN layer on the buffer layer; forming an N-type GaN layer onthe GaN layer; forming a GaN layer having indium on the N-type GaNlayer; forming an active layer on the GaN layer having indium; andforming a P-type GaN layer on the active layer.

Here, after the GaN layer having indium is formed, a GaN layer issubsequently formed at a thickness of 10-30 Å, and the active layer isformed in 1 period to 7 periods under a temperature condition of600-800° C.

Also, after the active layer is formed, the P-type GaN layer is formedat a thickness of 750-1500 Å at a temperature of 980-1020° C.

According to the present invention, the InGaN layer having a lowconcentration of indium is formed between the N-type GaN layer and theactive layer formed on the sapphire substrate, so that deterioration oflight efficiency due to inconsistency of a lattice constant between theGaN layer and the active layer is prevented and the light efficiency canbe improved.

Also, the InGaN layer having a low Indium composition has a threedimensional structure on its surface and such three-dimensional growthof the surface can improve the light efficiency even more.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating a process for fabricating an LED accordingto the related art;

FIGS. 2 a through 2 d are views illustrating a process for fabricatingan LED according to the present invention; and

FIG. 3 is a view schematically showing a P-type GaN layer formedaccording to a quantum well growing method among the method forfabricating the LED according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to accompanying drawings.

FIGS. 2 a through 2 d are views illustrating a process for fabricating alight emitting diode (LED) according to the present invention.

As shown in FIGS. 2 a through 2 d, a buffer layer 201 having anempirical formula of In(x)Ga(1-x)N is formed on a sapphire (Al₂O₃)substrate 200 at a temperature of 500-600° C., and an undoped GaN layer203 is grown up to a thickness of 1-3 μm on the buffer layer 201 at atemperature of 1000-1100° C. (FIG. 2 a).

Next, an N-type GaN layer 205 is grown up to a thickness of 1-3 μm onthe undoped GaN layer 203 at a temperature of 1000-1100° C. (FIG. 2 b).

After the N-type GaN layer 205 is formed, a GaN layer 207 having a lowmole of indium (In) is grown up at a temperature of 600-800° C. beforean active layer 209 is formed (FIG. 2 c).

The composition ratio of indium in the InGaN layer 207 is given byIn(x)Ga(1-x)N(0<x<0.2). The In(x)Ga(1-x)N(0<x<0.2) layer is grown up toa thickness of 50-200 Å.

After the InGaN layer 207 is formed, an active layer 209 is formed.

The active layer 209 is formed of GaN layer at a thickness of 10-30 Åand makes an electron tunnels into a quantum-well layer, therebypreventing holes from penetrating into the In(x)Ga(1-x)N(0<x<0.2) layer.

The active layer 209 of the InGaN/GaN having a multi-quantum-wellstructure is formed in 1 period to 7 periods at a temperature of600-800° C.

After the active layer 209 is formed, a P-type GaN layer 210 doped witha dopant of magnesium (Mg) is formed grown up to a thickness of 750-1500Å at a temperature of 980-1020° C.

FIG. 3 is a view schematically showing a P-type GaN layer formedaccording to a quantum-well growing method among the method forfabricating the LED according to the present invention.

As shown in FIG. 3, in the quantum-well growing method, a well growingstep of forming a well layer 301 that includes various dopants such asIn, Ga, and N is performed. Here, a growth condition of the well layer301 is given by TMGa: 0-200 μmol/min, TMIn: 0-100 μmol/min , NH₃: 0-80L/min, growing temperature: 600-800° C.

Subsequently, an enough crystal time is given so that the dopantsincluded in the step of growing the well layer 301 may combine eachother completely to form a crystal layer 302, whereby a combiningability of In and N, Ga and N, In and Ga inside the well layer 301, isimproved.

Here, a growth time of the crystal layer 302 is given by 0.1 sec-60 minand N₂: 30-50 L/min, H₂: 30 -50 L/min.

Next, a barrier growing step of forming a barrier layer 303 includingvarious dopants such as Ga, N, is performed. Here, a growth condition ofthe barrier layer 303 is given by TMGa: 100-500 μmol/min, TMIn: 50-200μmol/min , NH₃: 0-80 L/min, growing temperature: 600-800° C.

As described above, the active layer 209 is formed so as to have amulti-quantum well structure in the present invention, and the GaN layer207 having the low concentration of indium is formed in a shallowthickness on the N-type GaN layer 205 at a low temperature, so thatinconsistency of the lattice constant with the active layer 209 isreduced and light efficiency can be improved.

Also, since the InGaN layer of the active layer 209 is formed through athree-dimensional growth, a brightness of light generated at the activelayer 209 is increased.

INDUSTRIAL APPLICABILITY

As described above in detail, the present invention forms the InGaNlayer having a low concentration of indium between the N-type GaN layerand the active layer formed on the sapphire substrate, thereby reducinginconsistency of the lattice constant with the active layer andimproving light efficiency.

Further, the InGaN layer having the low concentration of indium, has athree dimensional structure on its surface, and light efficiency can beimproved even more in case a surface has such a three-dimensionalstructure.

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention that come within thescope of the appended claims and their equivalents.

1. A method for fabricating a light emitting diode, comprising: forminga first conductive type semiconductor layer; forming at least one GaNlayer having indium on the first conductive type semiconductor layer;forming at least one GaN layer directly on the GaN layer having indium;forming an active layer directly on the GaN layer; and forming a secondconductive type semiconductor layer on the active layer, wherein thesecond conductive type semiconductor layer has a thickness of 750-1500Å.
 2. The method according to claim 1, wherein an empirical formula ofthe GaN layer having indium is given by In_(x)Ga_(1-x)N and a range of xis given by 0<x<0.2.
 3. The method according to claim 1, wherein theactive layer is formed of a multi-quantum well structure having anInGaN/GaN structure.
 4. The method according to claim 1, wherein athickness of the GaN layer is 10-30 Å.
 5. The method according to claim1, wherein a thickness of the first conductive type semiconductor layeris 1-3 μm.
 6. The method according to claim 1, wherein the active layerincludes at least one well layer and at least one barrier layer formedin 1 period to 7 periods.
 7. The method according to claim 1, furthercomprising: preparing a substrate; forming a buffer layer on thesubstrate; and forming a first GaN layer on the buffer layer.
 8. Themethod according to claim 7, wherein the buffer layer is formed ofGaN-based material.
 9. The method according to claim 7, wherein athickness of the first GaN layer is 1-3 μm.
 10. The method according toclaim 7, wherein a total thickness of the first GaN layer and the firstconductive type semiconductor layer is 2-6μm.
 11. The method accordingto claim 7, wherein the first GaN layer includes an undoped GaN layer.12. The method according to claim 1, further comprising: forming atransparent metal on the second conductive type semiconductor layer,wherein the transparent metal is ITO (Indium-Tin-Oxide).
 13. The methodaccording to claim 1, wherein the second conductive type semiconductorlayer includes at least one well layer and at least one barrier layer.14. The method according to claim 1, wherein the GaN layer having indiumhas a thickness less than 200 Å.
 15. The method according to claim 14,wherein the GaN layer having indium has a thickness greater than 50 Åand less than 200 Å.
 16. A method for fabricating a light emittingdiode, comprising: preparing a substrate; forming a buffer layer on thesubstrate; forming a first GaN layer on the buffer layer; forming afirst conductive type semiconductor layer on the first GaN layer;forming at least one GaN layer having indium on the first conductivetype semiconductor layer; forming at least one second GaN layer directlyon the GaN layer having indium; forming an active layer directly on thesecond GaN layer; and forming a second conductive type semiconductorlayer on the active layer, wherein a total thickness of the first GaNlayer and the first conductive type semiconductor layer is 2-6 μm. 17.The method according to claim 16, wherein a thickness of the second GaNlayer is 10-30 Å.
 18. The method according to claim 16, wherein the GaNlayer having indium has a thickness less than 200 Å.
 19. The methodaccording to claim 18, wherein the GaN layer having indium has athickness greater than 50 Å and less than 200 Å.
 20. A method forfabricating a light emitting diode, comprising: forming a firstconductive type semiconductor layer; forming at least one GaN layerhaving indium on the first conductive type semiconductor layer; formingat least one GaN layer directly on the GaN layer having indium, whereinthe GaN layer has a thickness of 10-30 Å; forming an active layerincluding InGaN directly on the GaN layer, wherein the active layerincludes at least one well layer and at least one barrier layer; andforming a second conductive type semiconductor layer on the activelayer, wherein the second conductive type semiconductor layer has athickness of 750-1500 Å.